1. Field of the Invention
One aspect of the present invention relates to a dispersive device and a wavelength selective switch.
2. Related Background Art
Japanese Patent Application Laid-Open Publication No. 2007-163780 discloses a multi-wavelength dispersive device applied to a wavelength selective switch. This device has two diffraction gratings. The first diffraction grating has an identical diffraction efficiency for p-polarized light and s-polarized light on the short wavelength side of an operating wavelength range and the second diffraction grating has an identical diffraction efficiency for p-polarized light and s-polarized light on the long wavelength side of the operating wavelength range. This configuration is intended to increase the angular dispersion and cancel out the wavelength dependence of diffraction efficiency, thereby reducing the wavelength dependence of diffraction efficiency.
U.S. Pat. Published Application No. 2009/0154876 describes a wavelength dispersive device having temperature compensation means. This wavelength dispersive device further has a prism for temperature compensation, in addition to an ordinary dispersive optical system. The prism for temperature compensation is disposed on optical paths of respective wavelength components dispersed by a diffraction grating.